IndVarSimplify.cpp revision c5ecbdc1896f1cc089372feef3191ace2f840898
1//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This transformation analyzes and transforms the induction variables (and 11// computations derived from them) into simpler forms suitable for subsequent 12// analysis and transformation. 13// 14// This transformation makes the following changes to each loop with an 15// identifiable induction variable: 16// 1. All loops are transformed to have a SINGLE canonical induction variable 17// which starts at zero and steps by one. 18// 2. The canonical induction variable is guaranteed to be the first PHI node 19// in the loop header block. 20// 3. The canonical induction variable is guaranteed to be in a wide enough 21// type so that IV expressions need not be (directly) zero-extended or 22// sign-extended. 23// 4. Any pointer arithmetic recurrences are raised to use array subscripts. 24// 25// If the trip count of a loop is computable, this pass also makes the following 26// changes: 27// 1. The exit condition for the loop is canonicalized to compare the 28// induction value against the exit value. This turns loops like: 29// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)' 30// 2. Any use outside of the loop of an expression derived from the indvar 31// is changed to compute the derived value outside of the loop, eliminating 32// the dependence on the exit value of the induction variable. If the only 33// purpose of the loop is to compute the exit value of some derived 34// expression, this transformation will make the loop dead. 35// 36// This transformation should be followed by strength reduction after all of the 37// desired loop transformations have been performed. 38// 39//===----------------------------------------------------------------------===// 40 41#define DEBUG_TYPE "indvars" 42#include "llvm/Transforms/Scalar.h" 43#include "llvm/BasicBlock.h" 44#include "llvm/Constants.h" 45#include "llvm/Instructions.h" 46#include "llvm/IntrinsicInst.h" 47#include "llvm/LLVMContext.h" 48#include "llvm/Type.h" 49#include "llvm/Analysis/Dominators.h" 50#include "llvm/Analysis/IVUsers.h" 51#include "llvm/Analysis/ScalarEvolutionExpander.h" 52#include "llvm/Analysis/LoopInfo.h" 53#include "llvm/Analysis/LoopPass.h" 54#include "llvm/Support/CFG.h" 55#include "llvm/Support/CommandLine.h" 56#include "llvm/Support/Debug.h" 57#include "llvm/Support/raw_ostream.h" 58#include "llvm/Transforms/Utils/Local.h" 59#include "llvm/Transforms/Utils/BasicBlockUtils.h" 60#include "llvm/Target/TargetData.h" 61#include "llvm/ADT/SmallVector.h" 62#include "llvm/ADT/Statistic.h" 63#include "llvm/ADT/STLExtras.h" 64using namespace llvm; 65 66STATISTIC(NumRemoved , "Number of aux indvars removed"); 67STATISTIC(NumWidened , "Number of indvars widened"); 68STATISTIC(NumInserted , "Number of canonical indvars added"); 69STATISTIC(NumReplaced , "Number of exit values replaced"); 70STATISTIC(NumLFTR , "Number of loop exit tests replaced"); 71STATISTIC(NumElimIdentity, "Number of IV identities eliminated"); 72STATISTIC(NumElimExt , "Number of IV sign/zero extends eliminated"); 73STATISTIC(NumElimRem , "Number of IV remainder operations eliminated"); 74STATISTIC(NumElimCmp , "Number of IV comparisons eliminated"); 75 76static cl::opt<bool> DisableIVRewrite( 77 "disable-iv-rewrite", cl::Hidden, 78 cl::desc("Disable canonical induction variable rewriting")); 79 80namespace { 81 class IndVarSimplify : public LoopPass { 82 IVUsers *IU; 83 LoopInfo *LI; 84 ScalarEvolution *SE; 85 DominatorTree *DT; 86 TargetData *TD; 87 88 SmallVector<WeakVH, 16> DeadInsts; 89 bool Changed; 90 public: 91 92 static char ID; // Pass identification, replacement for typeid 93 IndVarSimplify() : LoopPass(ID), IU(0), LI(0), SE(0), DT(0), TD(0), 94 Changed(false) { 95 initializeIndVarSimplifyPass(*PassRegistry::getPassRegistry()); 96 } 97 98 virtual bool runOnLoop(Loop *L, LPPassManager &LPM); 99 100 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 101 AU.addRequired<DominatorTree>(); 102 AU.addRequired<LoopInfo>(); 103 AU.addRequired<ScalarEvolution>(); 104 AU.addRequiredID(LoopSimplifyID); 105 AU.addRequiredID(LCSSAID); 106 if (!DisableIVRewrite) 107 AU.addRequired<IVUsers>(); 108 AU.addPreserved<ScalarEvolution>(); 109 AU.addPreservedID(LoopSimplifyID); 110 AU.addPreservedID(LCSSAID); 111 if (!DisableIVRewrite) 112 AU.addPreserved<IVUsers>(); 113 AU.setPreservesCFG(); 114 } 115 116 private: 117 bool isValidRewrite(Value *FromVal, Value *ToVal); 118 119 void SimplifyIVUsers(SCEVExpander &Rewriter); 120 void SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter); 121 122 bool EliminateIVUser(Instruction *UseInst, Instruction *IVOperand); 123 void EliminateIVComparison(ICmpInst *ICmp, Value *IVOperand); 124 void EliminateIVRemainder(BinaryOperator *Rem, 125 Value *IVOperand, 126 bool IsSigned); 127 bool isSimpleIVUser(Instruction *I, const Loop *L); 128 void RewriteNonIntegerIVs(Loop *L); 129 130 ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount, 131 PHINode *IndVar, 132 SCEVExpander &Rewriter); 133 134 void RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter); 135 136 void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter); 137 138 void SinkUnusedInvariants(Loop *L); 139 140 void HandleFloatingPointIV(Loop *L, PHINode *PH); 141 }; 142} 143 144char IndVarSimplify::ID = 0; 145INITIALIZE_PASS_BEGIN(IndVarSimplify, "indvars", 146 "Induction Variable Simplification", false, false) 147INITIALIZE_PASS_DEPENDENCY(DominatorTree) 148INITIALIZE_PASS_DEPENDENCY(LoopInfo) 149INITIALIZE_PASS_DEPENDENCY(ScalarEvolution) 150INITIALIZE_PASS_DEPENDENCY(LoopSimplify) 151INITIALIZE_PASS_DEPENDENCY(LCSSA) 152INITIALIZE_PASS_DEPENDENCY(IVUsers) 153INITIALIZE_PASS_END(IndVarSimplify, "indvars", 154 "Induction Variable Simplification", false, false) 155 156Pass *llvm::createIndVarSimplifyPass() { 157 return new IndVarSimplify(); 158} 159 160/// isValidRewrite - Return true if the SCEV expansion generated by the 161/// rewriter can replace the original value. SCEV guarantees that it 162/// produces the same value, but the way it is produced may be illegal IR. 163/// Ideally, this function will only be called for verification. 164bool IndVarSimplify::isValidRewrite(Value *FromVal, Value *ToVal) { 165 // If an SCEV expression subsumed multiple pointers, its expansion could 166 // reassociate the GEP changing the base pointer. This is illegal because the 167 // final address produced by a GEP chain must be inbounds relative to its 168 // underlying object. Otherwise basic alias analysis, among other things, 169 // could fail in a dangerous way. Ultimately, SCEV will be improved to avoid 170 // producing an expression involving multiple pointers. Until then, we must 171 // bail out here. 172 // 173 // Retrieve the pointer operand of the GEP. Don't use GetUnderlyingObject 174 // because it understands lcssa phis while SCEV does not. 175 Value *FromPtr = FromVal; 176 Value *ToPtr = ToVal; 177 if (GEPOperator *GEP = dyn_cast<GEPOperator>(FromVal)) { 178 FromPtr = GEP->getPointerOperand(); 179 } 180 if (GEPOperator *GEP = dyn_cast<GEPOperator>(ToVal)) { 181 ToPtr = GEP->getPointerOperand(); 182 } 183 if (FromPtr != FromVal || ToPtr != ToVal) { 184 // Quickly check the common case 185 if (FromPtr == ToPtr) 186 return true; 187 188 // SCEV may have rewritten an expression that produces the GEP's pointer 189 // operand. That's ok as long as the pointer operand has the same base 190 // pointer. Unlike GetUnderlyingObject(), getPointerBase() will find the 191 // base of a recurrence. This handles the case in which SCEV expansion 192 // converts a pointer type recurrence into a nonrecurrent pointer base 193 // indexed by an integer recurrence. 194 const SCEV *FromBase = SE->getPointerBase(SE->getSCEV(FromPtr)); 195 const SCEV *ToBase = SE->getPointerBase(SE->getSCEV(ToPtr)); 196 if (FromBase == ToBase) 197 return true; 198 199 DEBUG(dbgs() << "INDVARS: GEP rewrite bail out " 200 << *FromBase << " != " << *ToBase << "\n"); 201 202 return false; 203 } 204 return true; 205} 206 207/// canExpandBackedgeTakenCount - Return true if this loop's backedge taken 208/// count expression can be safely and cheaply expanded into an instruction 209/// sequence that can be used by LinearFunctionTestReplace. 210static bool canExpandBackedgeTakenCount(Loop *L, ScalarEvolution *SE) { 211 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); 212 if (isa<SCEVCouldNotCompute>(BackedgeTakenCount) || 213 BackedgeTakenCount->isZero()) 214 return false; 215 216 if (!L->getExitingBlock()) 217 return false; 218 219 // Can't rewrite non-branch yet. 220 BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); 221 if (!BI) 222 return false; 223 224 // Special case: If the backedge-taken count is a UDiv, it's very likely a 225 // UDiv that ScalarEvolution produced in order to compute a precise 226 // expression, rather than a UDiv from the user's code. If we can't find a 227 // UDiv in the code with some simple searching, assume the former and forego 228 // rewriting the loop. 229 if (isa<SCEVUDivExpr>(BackedgeTakenCount)) { 230 ICmpInst *OrigCond = dyn_cast<ICmpInst>(BI->getCondition()); 231 if (!OrigCond) return false; 232 const SCEV *R = SE->getSCEV(OrigCond->getOperand(1)); 233 R = SE->getMinusSCEV(R, SE->getConstant(R->getType(), 1)); 234 if (R != BackedgeTakenCount) { 235 const SCEV *L = SE->getSCEV(OrigCond->getOperand(0)); 236 L = SE->getMinusSCEV(L, SE->getConstant(L->getType(), 1)); 237 if (L != BackedgeTakenCount) 238 return false; 239 } 240 } 241 return true; 242} 243 244/// getBackedgeIVType - Get the widest type used by the loop test after peeking 245/// through Truncs. 246/// 247/// TODO: Unnecessary once LinearFunctionTestReplace is removed. 248static const Type *getBackedgeIVType(Loop *L) { 249 if (!L->getExitingBlock()) 250 return 0; 251 252 // Can't rewrite non-branch yet. 253 BranchInst *BI = dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator()); 254 if (!BI) 255 return 0; 256 257 ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition()); 258 if (!Cond) 259 return 0; 260 261 const Type *Ty = 0; 262 for(User::op_iterator OI = Cond->op_begin(), OE = Cond->op_end(); 263 OI != OE; ++OI) { 264 assert((!Ty || Ty == (*OI)->getType()) && "bad icmp operand types"); 265 TruncInst *Trunc = dyn_cast<TruncInst>(*OI); 266 if (!Trunc) 267 continue; 268 269 return Trunc->getSrcTy(); 270 } 271 return Ty; 272} 273 274/// LinearFunctionTestReplace - This method rewrites the exit condition of the 275/// loop to be a canonical != comparison against the incremented loop induction 276/// variable. This pass is able to rewrite the exit tests of any loop where the 277/// SCEV analysis can determine a loop-invariant trip count of the loop, which 278/// is actually a much broader range than just linear tests. 279ICmpInst *IndVarSimplify:: 280LinearFunctionTestReplace(Loop *L, 281 const SCEV *BackedgeTakenCount, 282 PHINode *IndVar, 283 SCEVExpander &Rewriter) { 284 assert(canExpandBackedgeTakenCount(L, SE) && "precondition"); 285 BranchInst *BI = cast<BranchInst>(L->getExitingBlock()->getTerminator()); 286 287 // If the exiting block is not the same as the backedge block, we must compare 288 // against the preincremented value, otherwise we prefer to compare against 289 // the post-incremented value. 290 Value *CmpIndVar; 291 const SCEV *RHS = BackedgeTakenCount; 292 if (L->getExitingBlock() == L->getLoopLatch()) { 293 // Add one to the "backedge-taken" count to get the trip count. 294 // If this addition may overflow, we have to be more pessimistic and 295 // cast the induction variable before doing the add. 296 const SCEV *Zero = SE->getConstant(BackedgeTakenCount->getType(), 0); 297 const SCEV *N = 298 SE->getAddExpr(BackedgeTakenCount, 299 SE->getConstant(BackedgeTakenCount->getType(), 1)); 300 if ((isa<SCEVConstant>(N) && !N->isZero()) || 301 SE->isLoopEntryGuardedByCond(L, ICmpInst::ICMP_NE, N, Zero)) { 302 // No overflow. Cast the sum. 303 RHS = SE->getTruncateOrZeroExtend(N, IndVar->getType()); 304 } else { 305 // Potential overflow. Cast before doing the add. 306 RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, 307 IndVar->getType()); 308 RHS = SE->getAddExpr(RHS, 309 SE->getConstant(IndVar->getType(), 1)); 310 } 311 312 // The BackedgeTaken expression contains the number of times that the 313 // backedge branches to the loop header. This is one less than the 314 // number of times the loop executes, so use the incremented indvar. 315 CmpIndVar = IndVar->getIncomingValueForBlock(L->getExitingBlock()); 316 } else { 317 // We have to use the preincremented value... 318 RHS = SE->getTruncateOrZeroExtend(BackedgeTakenCount, 319 IndVar->getType()); 320 CmpIndVar = IndVar; 321 } 322 323 // Expand the code for the iteration count. 324 assert(SE->isLoopInvariant(RHS, L) && 325 "Computed iteration count is not loop invariant!"); 326 Value *ExitCnt = Rewriter.expandCodeFor(RHS, IndVar->getType(), BI); 327 328 // Insert a new icmp_ne or icmp_eq instruction before the branch. 329 ICmpInst::Predicate Opcode; 330 if (L->contains(BI->getSuccessor(0))) 331 Opcode = ICmpInst::ICMP_NE; 332 else 333 Opcode = ICmpInst::ICMP_EQ; 334 335 DEBUG(dbgs() << "INDVARS: Rewriting loop exit condition to:\n" 336 << " LHS:" << *CmpIndVar << '\n' 337 << " op:\t" 338 << (Opcode == ICmpInst::ICMP_NE ? "!=" : "==") << "\n" 339 << " RHS:\t" << *RHS << "\n"); 340 341 ICmpInst *Cond = new ICmpInst(BI, Opcode, CmpIndVar, ExitCnt, "exitcond"); 342 Cond->setDebugLoc(BI->getDebugLoc()); 343 Value *OrigCond = BI->getCondition(); 344 // It's tempting to use replaceAllUsesWith here to fully replace the old 345 // comparison, but that's not immediately safe, since users of the old 346 // comparison may not be dominated by the new comparison. Instead, just 347 // update the branch to use the new comparison; in the common case this 348 // will make old comparison dead. 349 BI->setCondition(Cond); 350 DeadInsts.push_back(OrigCond); 351 352 ++NumLFTR; 353 Changed = true; 354 return Cond; 355} 356 357/// RewriteLoopExitValues - Check to see if this loop has a computable 358/// loop-invariant execution count. If so, this means that we can compute the 359/// final value of any expressions that are recurrent in the loop, and 360/// substitute the exit values from the loop into any instructions outside of 361/// the loop that use the final values of the current expressions. 362/// 363/// This is mostly redundant with the regular IndVarSimplify activities that 364/// happen later, except that it's more powerful in some cases, because it's 365/// able to brute-force evaluate arbitrary instructions as long as they have 366/// constant operands at the beginning of the loop. 367void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) { 368 // Verify the input to the pass in already in LCSSA form. 369 assert(L->isLCSSAForm(*DT)); 370 371 SmallVector<BasicBlock*, 8> ExitBlocks; 372 L->getUniqueExitBlocks(ExitBlocks); 373 374 // Find all values that are computed inside the loop, but used outside of it. 375 // Because of LCSSA, these values will only occur in LCSSA PHI Nodes. Scan 376 // the exit blocks of the loop to find them. 377 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) { 378 BasicBlock *ExitBB = ExitBlocks[i]; 379 380 // If there are no PHI nodes in this exit block, then no values defined 381 // inside the loop are used on this path, skip it. 382 PHINode *PN = dyn_cast<PHINode>(ExitBB->begin()); 383 if (!PN) continue; 384 385 unsigned NumPreds = PN->getNumIncomingValues(); 386 387 // Iterate over all of the PHI nodes. 388 BasicBlock::iterator BBI = ExitBB->begin(); 389 while ((PN = dyn_cast<PHINode>(BBI++))) { 390 if (PN->use_empty()) 391 continue; // dead use, don't replace it 392 393 // SCEV only supports integer expressions for now. 394 if (!PN->getType()->isIntegerTy() && !PN->getType()->isPointerTy()) 395 continue; 396 397 // It's necessary to tell ScalarEvolution about this explicitly so that 398 // it can walk the def-use list and forget all SCEVs, as it may not be 399 // watching the PHI itself. Once the new exit value is in place, there 400 // may not be a def-use connection between the loop and every instruction 401 // which got a SCEVAddRecExpr for that loop. 402 SE->forgetValue(PN); 403 404 // Iterate over all of the values in all the PHI nodes. 405 for (unsigned i = 0; i != NumPreds; ++i) { 406 // If the value being merged in is not integer or is not defined 407 // in the loop, skip it. 408 Value *InVal = PN->getIncomingValue(i); 409 if (!isa<Instruction>(InVal)) 410 continue; 411 412 // If this pred is for a subloop, not L itself, skip it. 413 if (LI->getLoopFor(PN->getIncomingBlock(i)) != L) 414 continue; // The Block is in a subloop, skip it. 415 416 // Check that InVal is defined in the loop. 417 Instruction *Inst = cast<Instruction>(InVal); 418 if (!L->contains(Inst)) 419 continue; 420 421 // Okay, this instruction has a user outside of the current loop 422 // and varies predictably *inside* the loop. Evaluate the value it 423 // contains when the loop exits, if possible. 424 const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop()); 425 if (!SE->isLoopInvariant(ExitValue, L)) 426 continue; 427 428 Value *ExitVal = Rewriter.expandCodeFor(ExitValue, PN->getType(), Inst); 429 430 DEBUG(dbgs() << "INDVARS: RLEV: AfterLoopVal = " << *ExitVal << '\n' 431 << " LoopVal = " << *Inst << "\n"); 432 433 if (!isValidRewrite(Inst, ExitVal)) { 434 DeadInsts.push_back(ExitVal); 435 continue; 436 } 437 Changed = true; 438 ++NumReplaced; 439 440 PN->setIncomingValue(i, ExitVal); 441 442 // If this instruction is dead now, delete it. 443 RecursivelyDeleteTriviallyDeadInstructions(Inst); 444 445 if (NumPreds == 1) { 446 // Completely replace a single-pred PHI. This is safe, because the 447 // NewVal won't be variant in the loop, so we don't need an LCSSA phi 448 // node anymore. 449 PN->replaceAllUsesWith(ExitVal); 450 RecursivelyDeleteTriviallyDeadInstructions(PN); 451 } 452 } 453 if (NumPreds != 1) { 454 // Clone the PHI and delete the original one. This lets IVUsers and 455 // any other maps purge the original user from their records. 456 PHINode *NewPN = cast<PHINode>(PN->clone()); 457 NewPN->takeName(PN); 458 NewPN->insertBefore(PN); 459 PN->replaceAllUsesWith(NewPN); 460 PN->eraseFromParent(); 461 } 462 } 463 } 464 465 // The insertion point instruction may have been deleted; clear it out 466 // so that the rewriter doesn't trip over it later. 467 Rewriter.clearInsertPoint(); 468} 469 470void IndVarSimplify::RewriteNonIntegerIVs(Loop *L) { 471 // First step. Check to see if there are any floating-point recurrences. 472 // If there are, change them into integer recurrences, permitting analysis by 473 // the SCEV routines. 474 // 475 BasicBlock *Header = L->getHeader(); 476 477 SmallVector<WeakVH, 8> PHIs; 478 for (BasicBlock::iterator I = Header->begin(); 479 PHINode *PN = dyn_cast<PHINode>(I); ++I) 480 PHIs.push_back(PN); 481 482 for (unsigned i = 0, e = PHIs.size(); i != e; ++i) 483 if (PHINode *PN = dyn_cast_or_null<PHINode>(&*PHIs[i])) 484 HandleFloatingPointIV(L, PN); 485 486 // If the loop previously had floating-point IV, ScalarEvolution 487 // may not have been able to compute a trip count. Now that we've done some 488 // re-writing, the trip count may be computable. 489 if (Changed) 490 SE->forgetLoop(L); 491} 492 493/// SimplifyIVUsers - Iteratively perform simplification on IVUsers within this 494/// loop. IVUsers is treated as a worklist. Each successive simplification may 495/// push more users which may themselves be candidates for simplification. 496/// 497/// This is the old approach to IV simplification to be replaced by 498/// SimplifyIVUsersNoRewrite. 499/// 500void IndVarSimplify::SimplifyIVUsers(SCEVExpander &Rewriter) { 501 // Each round of simplification involves a round of eliminating operations 502 // followed by a round of widening IVs. A single IVUsers worklist is used 503 // across all rounds. The inner loop advances the user. If widening exposes 504 // more uses, then another pass through the outer loop is triggered. 505 for (IVUsers::iterator I = IU->begin(); I != IU->end(); ++I) { 506 Instruction *UseInst = I->getUser(); 507 Value *IVOperand = I->getOperandValToReplace(); 508 509 if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) { 510 EliminateIVComparison(ICmp, IVOperand); 511 continue; 512 } 513 if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) { 514 bool IsSigned = Rem->getOpcode() == Instruction::SRem; 515 if (IsSigned || Rem->getOpcode() == Instruction::URem) { 516 EliminateIVRemainder(Rem, IVOperand, IsSigned); 517 continue; 518 } 519 } 520 } 521} 522 523namespace { 524 // Collect information about induction variables that are used by sign/zero 525 // extend operations. This information is recorded by CollectExtend and 526 // provides the input to WidenIV. 527 struct WideIVInfo { 528 const Type *WidestNativeType; // Widest integer type created [sz]ext 529 bool IsSigned; // Was an sext user seen before a zext? 530 531 WideIVInfo() : WidestNativeType(0), IsSigned(false) {} 532 }; 533} 534 535/// CollectExtend - Update information about the induction variable that is 536/// extended by this sign or zero extend operation. This is used to determine 537/// the final width of the IV before actually widening it. 538static void CollectExtend(CastInst *Cast, bool IsSigned, WideIVInfo &WI, 539 ScalarEvolution *SE, const TargetData *TD) { 540 const Type *Ty = Cast->getType(); 541 uint64_t Width = SE->getTypeSizeInBits(Ty); 542 if (TD && !TD->isLegalInteger(Width)) 543 return; 544 545 if (!WI.WidestNativeType) { 546 WI.WidestNativeType = SE->getEffectiveSCEVType(Ty); 547 WI.IsSigned = IsSigned; 548 return; 549 } 550 551 // We extend the IV to satisfy the sign of its first user, arbitrarily. 552 if (WI.IsSigned != IsSigned) 553 return; 554 555 if (Width > SE->getTypeSizeInBits(WI.WidestNativeType)) 556 WI.WidestNativeType = SE->getEffectiveSCEVType(Ty); 557} 558 559namespace { 560/// WidenIV - The goal of this transform is to remove sign and zero extends 561/// without creating any new induction variables. To do this, it creates a new 562/// phi of the wider type and redirects all users, either removing extends or 563/// inserting truncs whenever we stop propagating the type. 564/// 565class WidenIV { 566 // Parameters 567 PHINode *OrigPhi; 568 const Type *WideType; 569 bool IsSigned; 570 571 // Context 572 LoopInfo *LI; 573 Loop *L; 574 ScalarEvolution *SE; 575 DominatorTree *DT; 576 577 // Result 578 PHINode *WidePhi; 579 Instruction *WideInc; 580 const SCEV *WideIncExpr; 581 SmallVectorImpl<WeakVH> &DeadInsts; 582 583 SmallPtrSet<Instruction*,16> Widened; 584 SmallVector<std::pair<Use *, Instruction *>, 8> NarrowIVUsers; 585 586public: 587 WidenIV(PHINode *PN, const WideIVInfo &WI, LoopInfo *LInfo, 588 ScalarEvolution *SEv, DominatorTree *DTree, 589 SmallVectorImpl<WeakVH> &DI) : 590 OrigPhi(PN), 591 WideType(WI.WidestNativeType), 592 IsSigned(WI.IsSigned), 593 LI(LInfo), 594 L(LI->getLoopFor(OrigPhi->getParent())), 595 SE(SEv), 596 DT(DTree), 597 WidePhi(0), 598 WideInc(0), 599 WideIncExpr(0), 600 DeadInsts(DI) { 601 assert(L->getHeader() == OrigPhi->getParent() && "Phi must be an IV"); 602 } 603 604 PHINode *CreateWideIV(SCEVExpander &Rewriter); 605 606protected: 607 Instruction *CloneIVUser(Instruction *NarrowUse, 608 Instruction *NarrowDef, 609 Instruction *WideDef); 610 611 const SCEVAddRecExpr *GetWideRecurrence(Instruction *NarrowUse); 612 613 Instruction *WidenIVUse(Use &NarrowDefUse, Instruction *NarrowDef, 614 Instruction *WideDef); 615 616 void pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef); 617}; 618} // anonymous namespace 619 620static Value *getExtend( Value *NarrowOper, const Type *WideType, 621 bool IsSigned, IRBuilder<> &Builder) { 622 return IsSigned ? Builder.CreateSExt(NarrowOper, WideType) : 623 Builder.CreateZExt(NarrowOper, WideType); 624} 625 626/// CloneIVUser - Instantiate a wide operation to replace a narrow 627/// operation. This only needs to handle operations that can evaluation to 628/// SCEVAddRec. It can safely return 0 for any operation we decide not to clone. 629Instruction *WidenIV::CloneIVUser(Instruction *NarrowUse, 630 Instruction *NarrowDef, 631 Instruction *WideDef) { 632 unsigned Opcode = NarrowUse->getOpcode(); 633 switch (Opcode) { 634 default: 635 return 0; 636 case Instruction::Add: 637 case Instruction::Mul: 638 case Instruction::UDiv: 639 case Instruction::Sub: 640 case Instruction::And: 641 case Instruction::Or: 642 case Instruction::Xor: 643 case Instruction::Shl: 644 case Instruction::LShr: 645 case Instruction::AShr: 646 DEBUG(dbgs() << "Cloning IVUser: " << *NarrowUse << "\n"); 647 648 IRBuilder<> Builder(NarrowUse); 649 650 // Replace NarrowDef operands with WideDef. Otherwise, we don't know 651 // anything about the narrow operand yet so must insert a [sz]ext. It is 652 // probably loop invariant and will be folded or hoisted. If it actually 653 // comes from a widened IV, it should be removed during a future call to 654 // WidenIVUse. 655 Value *LHS = (NarrowUse->getOperand(0) == NarrowDef) ? WideDef : 656 getExtend(NarrowUse->getOperand(0), WideType, IsSigned, Builder); 657 Value *RHS = (NarrowUse->getOperand(1) == NarrowDef) ? WideDef : 658 getExtend(NarrowUse->getOperand(1), WideType, IsSigned, Builder); 659 660 BinaryOperator *NarrowBO = cast<BinaryOperator>(NarrowUse); 661 BinaryOperator *WideBO = BinaryOperator::Create(NarrowBO->getOpcode(), 662 LHS, RHS, 663 NarrowBO->getName()); 664 Builder.Insert(WideBO); 665 if (const OverflowingBinaryOperator *OBO = 666 dyn_cast<OverflowingBinaryOperator>(NarrowBO)) { 667 if (OBO->hasNoUnsignedWrap()) WideBO->setHasNoUnsignedWrap(); 668 if (OBO->hasNoSignedWrap()) WideBO->setHasNoSignedWrap(); 669 } 670 return WideBO; 671 } 672 llvm_unreachable(0); 673} 674 675/// HoistStep - Attempt to hoist an IV increment above a potential use. 676/// 677/// To successfully hoist, two criteria must be met: 678/// - IncV operands dominate InsertPos and 679/// - InsertPos dominates IncV 680/// 681/// Meeting the second condition means that we don't need to check all of IncV's 682/// existing uses (it's moving up in the domtree). 683/// 684/// This does not yet recursively hoist the operands, although that would 685/// not be difficult. 686static bool HoistStep(Instruction *IncV, Instruction *InsertPos, 687 const DominatorTree *DT) 688{ 689 if (DT->dominates(IncV, InsertPos)) 690 return true; 691 692 if (!DT->dominates(InsertPos->getParent(), IncV->getParent())) 693 return false; 694 695 if (IncV->mayHaveSideEffects()) 696 return false; 697 698 // Attempt to hoist IncV 699 for (User::op_iterator OI = IncV->op_begin(), OE = IncV->op_end(); 700 OI != OE; ++OI) { 701 Instruction *OInst = dyn_cast<Instruction>(OI); 702 if (OInst && !DT->dominates(OInst, InsertPos)) 703 return false; 704 } 705 IncV->moveBefore(InsertPos); 706 return true; 707} 708 709// GetWideRecurrence - Is this instruction potentially interesting from IVUsers' 710// perspective after widening it's type? In other words, can the extend be 711// safely hoisted out of the loop with SCEV reducing the value to a recurrence 712// on the same loop. If so, return the sign or zero extended 713// recurrence. Otherwise return NULL. 714const SCEVAddRecExpr *WidenIV::GetWideRecurrence(Instruction *NarrowUse) { 715 if (!SE->isSCEVable(NarrowUse->getType())) 716 return 0; 717 718 const SCEV *NarrowExpr = SE->getSCEV(NarrowUse); 719 if (SE->getTypeSizeInBits(NarrowExpr->getType()) 720 >= SE->getTypeSizeInBits(WideType)) { 721 // NarrowUse implicitly widens its operand. e.g. a gep with a narrow 722 // index. So don't follow this use. 723 return 0; 724 } 725 726 const SCEV *WideExpr = IsSigned ? 727 SE->getSignExtendExpr(NarrowExpr, WideType) : 728 SE->getZeroExtendExpr(NarrowExpr, WideType); 729 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(WideExpr); 730 if (!AddRec || AddRec->getLoop() != L) 731 return 0; 732 733 return AddRec; 734} 735 736/// WidenIVUse - Determine whether an individual user of the narrow IV can be 737/// widened. If so, return the wide clone of the user. 738Instruction *WidenIV::WidenIVUse(Use &NarrowDefUse, Instruction *NarrowDef, 739 Instruction *WideDef) { 740 Instruction *NarrowUse = cast<Instruction>(NarrowDefUse.getUser()); 741 742 // Stop traversing the def-use chain at inner-loop phis or post-loop phis. 743 if (isa<PHINode>(NarrowUse) && LI->getLoopFor(NarrowUse->getParent()) != L) 744 return 0; 745 746 // Our raison d'etre! Eliminate sign and zero extension. 747 if (IsSigned ? isa<SExtInst>(NarrowUse) : isa<ZExtInst>(NarrowUse)) { 748 Value *NewDef = WideDef; 749 if (NarrowUse->getType() != WideType) { 750 unsigned CastWidth = SE->getTypeSizeInBits(NarrowUse->getType()); 751 unsigned IVWidth = SE->getTypeSizeInBits(WideType); 752 if (CastWidth < IVWidth) { 753 // The cast isn't as wide as the IV, so insert a Trunc. 754 IRBuilder<> Builder(NarrowDefUse); 755 NewDef = Builder.CreateTrunc(WideDef, NarrowUse->getType()); 756 } 757 else { 758 // A wider extend was hidden behind a narrower one. This may induce 759 // another round of IV widening in which the intermediate IV becomes 760 // dead. It should be very rare. 761 DEBUG(dbgs() << "INDVARS: New IV " << *WidePhi 762 << " not wide enough to subsume " << *NarrowUse << "\n"); 763 NarrowUse->replaceUsesOfWith(NarrowDef, WideDef); 764 NewDef = NarrowUse; 765 } 766 } 767 if (NewDef != NarrowUse) { 768 DEBUG(dbgs() << "INDVARS: eliminating " << *NarrowUse 769 << " replaced by " << *WideDef << "\n"); 770 ++NumElimExt; 771 NarrowUse->replaceAllUsesWith(NewDef); 772 DeadInsts.push_back(NarrowUse); 773 } 774 // Now that the extend is gone, we want to expose it's uses for potential 775 // further simplification. We don't need to directly inform SimplifyIVUsers 776 // of the new users, because their parent IV will be processed later as a 777 // new loop phi. If we preserved IVUsers analysis, we would also want to 778 // push the uses of WideDef here. 779 780 // No further widening is needed. The deceased [sz]ext had done it for us. 781 return 0; 782 } 783 784 // Does this user itself evaluate to a recurrence after widening? 785 const SCEVAddRecExpr *WideAddRec = GetWideRecurrence(NarrowUse); 786 if (!WideAddRec) { 787 // This user does not evaluate to a recurence after widening, so don't 788 // follow it. Instead insert a Trunc to kill off the original use, 789 // eventually isolating the original narrow IV so it can be removed. 790 IRBuilder<> Builder(NarrowDefUse); 791 Value *Trunc = Builder.CreateTrunc(WideDef, NarrowDef->getType()); 792 NarrowUse->replaceUsesOfWith(NarrowDef, Trunc); 793 return 0; 794 } 795 // We assume that block terminators are not SCEVable. We wouldn't want to 796 // insert a Trunc after a terminator if there happens to be a critical edge. 797 assert(NarrowUse != NarrowUse->getParent()->getTerminator() && 798 "SCEV is not expected to evaluate a block terminator"); 799 800 // Reuse the IV increment that SCEVExpander created as long as it dominates 801 // NarrowUse. 802 Instruction *WideUse = 0; 803 if (WideAddRec == WideIncExpr && HoistStep(WideInc, NarrowUse, DT)) { 804 WideUse = WideInc; 805 } 806 else { 807 WideUse = CloneIVUser(NarrowUse, NarrowDef, WideDef); 808 if (!WideUse) 809 return 0; 810 } 811 // Evaluation of WideAddRec ensured that the narrow expression could be 812 // extended outside the loop without overflow. This suggests that the wide use 813 // evaluates to the same expression as the extended narrow use, but doesn't 814 // absolutely guarantee it. Hence the following failsafe check. In rare cases 815 // where it fails, we simply throw away the newly created wide use. 816 if (WideAddRec != SE->getSCEV(WideUse)) { 817 DEBUG(dbgs() << "Wide use expression mismatch: " << *WideUse 818 << ": " << *SE->getSCEV(WideUse) << " != " << *WideAddRec << "\n"); 819 DeadInsts.push_back(WideUse); 820 return 0; 821 } 822 823 // Returning WideUse pushes it on the worklist. 824 return WideUse; 825} 826 827/// pushNarrowIVUsers - Add eligible users of NarrowDef to NarrowIVUsers. 828/// 829void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) { 830 for (Value::use_iterator UI = NarrowDef->use_begin(), 831 UE = NarrowDef->use_end(); UI != UE; ++UI) { 832 Use &U = UI.getUse(); 833 834 // Handle data flow merges and bizarre phi cycles. 835 if (!Widened.insert(cast<Instruction>(U.getUser()))) 836 continue; 837 838 NarrowIVUsers.push_back(std::make_pair(&UI.getUse(), WideDef)); 839 } 840} 841 842/// CreateWideIV - Process a single induction variable. First use the 843/// SCEVExpander to create a wide induction variable that evaluates to the same 844/// recurrence as the original narrow IV. Then use a worklist to forward 845/// traverse the narrow IV's def-use chain. After WidenIVUse has processed all 846/// interesting IV users, the narrow IV will be isolated for removal by 847/// DeleteDeadPHIs. 848/// 849/// It would be simpler to delete uses as they are processed, but we must avoid 850/// invalidating SCEV expressions. 851/// 852PHINode *WidenIV::CreateWideIV(SCEVExpander &Rewriter) { 853 // Is this phi an induction variable? 854 const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(OrigPhi)); 855 if (!AddRec) 856 return NULL; 857 858 // Widen the induction variable expression. 859 const SCEV *WideIVExpr = IsSigned ? 860 SE->getSignExtendExpr(AddRec, WideType) : 861 SE->getZeroExtendExpr(AddRec, WideType); 862 863 assert(SE->getEffectiveSCEVType(WideIVExpr->getType()) == WideType && 864 "Expect the new IV expression to preserve its type"); 865 866 // Can the IV be extended outside the loop without overflow? 867 AddRec = dyn_cast<SCEVAddRecExpr>(WideIVExpr); 868 if (!AddRec || AddRec->getLoop() != L) 869 return NULL; 870 871 // An AddRec must have loop-invariant operands. Since this AddRec is 872 // materialized by a loop header phi, the expression cannot have any post-loop 873 // operands, so they must dominate the loop header. 874 assert(SE->properlyDominates(AddRec->getStart(), L->getHeader()) && 875 SE->properlyDominates(AddRec->getStepRecurrence(*SE), L->getHeader()) 876 && "Loop header phi recurrence inputs do not dominate the loop"); 877 878 // The rewriter provides a value for the desired IV expression. This may 879 // either find an existing phi or materialize a new one. Either way, we 880 // expect a well-formed cyclic phi-with-increments. i.e. any operand not part 881 // of the phi-SCC dominates the loop entry. 882 Instruction *InsertPt = L->getHeader()->begin(); 883 WidePhi = cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt)); 884 885 // Remembering the WideIV increment generated by SCEVExpander allows 886 // WidenIVUse to reuse it when widening the narrow IV's increment. We don't 887 // employ a general reuse mechanism because the call above is the only call to 888 // SCEVExpander. Henceforth, we produce 1-to-1 narrow to wide uses. 889 if (BasicBlock *LatchBlock = L->getLoopLatch()) { 890 WideInc = 891 cast<Instruction>(WidePhi->getIncomingValueForBlock(LatchBlock)); 892 WideIncExpr = SE->getSCEV(WideInc); 893 } 894 895 DEBUG(dbgs() << "Wide IV: " << *WidePhi << "\n"); 896 ++NumWidened; 897 898 // Traverse the def-use chain using a worklist starting at the original IV. 899 assert(Widened.empty() && NarrowIVUsers.empty() && "expect initial state" ); 900 901 Widened.insert(OrigPhi); 902 pushNarrowIVUsers(OrigPhi, WidePhi); 903 904 while (!NarrowIVUsers.empty()) { 905 Use *UsePtr; 906 Instruction *WideDef; 907 tie(UsePtr, WideDef) = NarrowIVUsers.pop_back_val(); 908 Use &NarrowDefUse = *UsePtr; 909 910 // Process a def-use edge. This may replace the use, so don't hold a 911 // use_iterator across it. 912 Instruction *NarrowDef = cast<Instruction>(NarrowDefUse.get()); 913 Instruction *WideUse = WidenIVUse(NarrowDefUse, NarrowDef, WideDef); 914 915 // Follow all def-use edges from the previous narrow use. 916 if (WideUse) 917 pushNarrowIVUsers(cast<Instruction>(NarrowDefUse.getUser()), WideUse); 918 919 // WidenIVUse may have removed the def-use edge. 920 if (NarrowDef->use_empty()) 921 DeadInsts.push_back(NarrowDef); 922 } 923 return WidePhi; 924} 925 926void IndVarSimplify::EliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) { 927 unsigned IVOperIdx = 0; 928 ICmpInst::Predicate Pred = ICmp->getPredicate(); 929 if (IVOperand != ICmp->getOperand(0)) { 930 // Swapped 931 assert(IVOperand == ICmp->getOperand(1) && "Can't find IVOperand"); 932 IVOperIdx = 1; 933 Pred = ICmpInst::getSwappedPredicate(Pred); 934 } 935 936 // Get the SCEVs for the ICmp operands. 937 const SCEV *S = SE->getSCEV(ICmp->getOperand(IVOperIdx)); 938 const SCEV *X = SE->getSCEV(ICmp->getOperand(1 - IVOperIdx)); 939 940 // Simplify unnecessary loops away. 941 const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent()); 942 S = SE->getSCEVAtScope(S, ICmpLoop); 943 X = SE->getSCEVAtScope(X, ICmpLoop); 944 945 // If the condition is always true or always false, replace it with 946 // a constant value. 947 if (SE->isKnownPredicate(Pred, S, X)) 948 ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext())); 949 else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X)) 950 ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext())); 951 else 952 return; 953 954 DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n'); 955 ++NumElimCmp; 956 Changed = true; 957 DeadInsts.push_back(ICmp); 958} 959 960void IndVarSimplify::EliminateIVRemainder(BinaryOperator *Rem, 961 Value *IVOperand, 962 bool IsSigned) { 963 // We're only interested in the case where we know something about 964 // the numerator. 965 if (IVOperand != Rem->getOperand(0)) 966 return; 967 968 // Get the SCEVs for the ICmp operands. 969 const SCEV *S = SE->getSCEV(Rem->getOperand(0)); 970 const SCEV *X = SE->getSCEV(Rem->getOperand(1)); 971 972 // Simplify unnecessary loops away. 973 const Loop *ICmpLoop = LI->getLoopFor(Rem->getParent()); 974 S = SE->getSCEVAtScope(S, ICmpLoop); 975 X = SE->getSCEVAtScope(X, ICmpLoop); 976 977 // i % n --> i if i is in [0,n). 978 if ((!IsSigned || SE->isKnownNonNegative(S)) && 979 SE->isKnownPredicate(IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, 980 S, X)) 981 Rem->replaceAllUsesWith(Rem->getOperand(0)); 982 else { 983 // (i+1) % n --> (i+1)==n?0:(i+1) if i is in [0,n). 984 const SCEV *LessOne = 985 SE->getMinusSCEV(S, SE->getConstant(S->getType(), 1)); 986 if (IsSigned && !SE->isKnownNonNegative(LessOne)) 987 return; 988 989 if (!SE->isKnownPredicate(IsSigned ? 990 ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, 991 LessOne, X)) 992 return; 993 994 ICmpInst *ICmp = new ICmpInst(Rem, ICmpInst::ICMP_EQ, 995 Rem->getOperand(0), Rem->getOperand(1), 996 "tmp"); 997 SelectInst *Sel = 998 SelectInst::Create(ICmp, 999 ConstantInt::get(Rem->getType(), 0), 1000 Rem->getOperand(0), "tmp", Rem); 1001 Rem->replaceAllUsesWith(Sel); 1002 } 1003 1004 // Inform IVUsers about the new users. 1005 if (IU) { 1006 if (Instruction *I = dyn_cast<Instruction>(Rem->getOperand(0))) 1007 IU->AddUsersIfInteresting(I); 1008 } 1009 DEBUG(dbgs() << "INDVARS: Simplified rem: " << *Rem << '\n'); 1010 ++NumElimRem; 1011 Changed = true; 1012 DeadInsts.push_back(Rem); 1013} 1014 1015/// EliminateIVUser - Eliminate an operation that consumes a simple IV and has 1016/// no observable side-effect given the range of IV values. 1017bool IndVarSimplify::EliminateIVUser(Instruction *UseInst, 1018 Instruction *IVOperand) { 1019 if (ICmpInst *ICmp = dyn_cast<ICmpInst>(UseInst)) { 1020 EliminateIVComparison(ICmp, IVOperand); 1021 return true; 1022 } 1023 if (BinaryOperator *Rem = dyn_cast<BinaryOperator>(UseInst)) { 1024 bool IsSigned = Rem->getOpcode() == Instruction::SRem; 1025 if (IsSigned || Rem->getOpcode() == Instruction::URem) { 1026 EliminateIVRemainder(Rem, IVOperand, IsSigned); 1027 return true; 1028 } 1029 } 1030 1031 // Eliminate any operation that SCEV can prove is an identity function. 1032 if (!SE->isSCEVable(UseInst->getType()) || 1033 (UseInst->getType() != IVOperand->getType()) || 1034 (SE->getSCEV(UseInst) != SE->getSCEV(IVOperand))) 1035 return false; 1036 1037 DEBUG(dbgs() << "INDVARS: Eliminated identity: " << *UseInst << '\n'); 1038 1039 UseInst->replaceAllUsesWith(IVOperand); 1040 ++NumElimIdentity; 1041 Changed = true; 1042 DeadInsts.push_back(UseInst); 1043 return true; 1044} 1045 1046/// pushIVUsers - Add all uses of Def to the current IV's worklist. 1047/// 1048static void pushIVUsers( 1049 Instruction *Def, 1050 SmallPtrSet<Instruction*,16> &Simplified, 1051 SmallVectorImpl< std::pair<Instruction*,Instruction*> > &SimpleIVUsers) { 1052 1053 for (Value::use_iterator UI = Def->use_begin(), E = Def->use_end(); 1054 UI != E; ++UI) { 1055 Instruction *User = cast<Instruction>(*UI); 1056 1057 // Avoid infinite or exponential worklist processing. 1058 // Also ensure unique worklist users. 1059 // If Def is a LoopPhi, it may not be in the Simplified set, so check for 1060 // self edges first. 1061 if (User != Def && Simplified.insert(User)) 1062 SimpleIVUsers.push_back(std::make_pair(User, Def)); 1063 } 1064} 1065 1066/// isSimpleIVUser - Return true if this instruction generates a simple SCEV 1067/// expression in terms of that IV. 1068/// 1069/// This is similar to IVUsers' isInsteresting() but processes each instruction 1070/// non-recursively when the operand is already known to be a simpleIVUser. 1071/// 1072bool IndVarSimplify::isSimpleIVUser(Instruction *I, const Loop *L) { 1073 if (!SE->isSCEVable(I->getType())) 1074 return false; 1075 1076 // Get the symbolic expression for this instruction. 1077 const SCEV *S = SE->getSCEV(I); 1078 1079 // We assume that terminators are not SCEVable. 1080 assert((!S || I != I->getParent()->getTerminator()) && 1081 "can't fold terminators"); 1082 1083 // Only consider affine recurrences. 1084 const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S); 1085 if (AR && AR->getLoop() == L) 1086 return true; 1087 1088 return false; 1089} 1090 1091/// SimplifyIVUsersNoRewrite - Iteratively perform simplification on a worklist 1092/// of IV users. Each successive simplification may push more users which may 1093/// themselves be candidates for simplification. 1094/// 1095/// The "NoRewrite" algorithm does not require IVUsers analysis. Instead, it 1096/// simplifies instructions in-place during analysis. Rather than rewriting 1097/// induction variables bottom-up from their users, it transforms a chain of 1098/// IVUsers top-down, updating the IR only when it encouters a clear 1099/// optimization opportunitiy. A SCEVExpander "Rewriter" instance is still 1100/// needed, but only used to generate a new IV (phi) of wider type for sign/zero 1101/// extend elimination. 1102/// 1103/// Once DisableIVRewrite is default, LSR will be the only client of IVUsers. 1104/// 1105void IndVarSimplify::SimplifyIVUsersNoRewrite(Loop *L, SCEVExpander &Rewriter) { 1106 std::map<PHINode *, WideIVInfo> WideIVMap; 1107 1108 SmallVector<PHINode*, 8> LoopPhis; 1109 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I) { 1110 LoopPhis.push_back(cast<PHINode>(I)); 1111 } 1112 // Each round of simplification iterates through the SimplifyIVUsers worklist 1113 // for all current phis, then determines whether any IVs can be 1114 // widened. Widening adds new phis to LoopPhis, inducing another round of 1115 // simplification on the wide IVs. 1116 while (!LoopPhis.empty()) { 1117 // Evaluate as many IV expressions as possible before widening any IVs. This 1118 // forces SCEV to set no-wrap flags before evaluating sign/zero 1119 // extension. The first time SCEV attempts to normalize sign/zero extension, 1120 // the result becomes final. So for the most predictable results, we delay 1121 // evaluation of sign/zero extend evaluation until needed, and avoid running 1122 // other SCEV based analysis prior to SimplifyIVUsersNoRewrite. 1123 do { 1124 PHINode *CurrIV = LoopPhis.pop_back_val(); 1125 1126 // Information about sign/zero extensions of CurrIV. 1127 WideIVInfo WI; 1128 1129 // Instructions processed by SimplifyIVUsers for CurrIV. 1130 SmallPtrSet<Instruction*,16> Simplified; 1131 1132 // Use-def pairs if IVUsers waiting to be processed for CurrIV. 1133 SmallVector<std::pair<Instruction*, Instruction*>, 8> SimpleIVUsers; 1134 1135 // Push users of the current LoopPhi. In rare cases, pushIVUsers may be 1136 // called multiple times for the same LoopPhi. This is the proper thing to 1137 // do for loop header phis that use each other. 1138 pushIVUsers(CurrIV, Simplified, SimpleIVUsers); 1139 1140 while (!SimpleIVUsers.empty()) { 1141 Instruction *UseInst, *Operand; 1142 tie(UseInst, Operand) = SimpleIVUsers.pop_back_val(); 1143 // Bypass back edges to avoid extra work. 1144 if (UseInst == CurrIV) continue; 1145 1146 if (EliminateIVUser(UseInst, Operand)) { 1147 pushIVUsers(Operand, Simplified, SimpleIVUsers); 1148 continue; 1149 } 1150 if (CastInst *Cast = dyn_cast<CastInst>(UseInst)) { 1151 bool IsSigned = Cast->getOpcode() == Instruction::SExt; 1152 if (IsSigned || Cast->getOpcode() == Instruction::ZExt) { 1153 CollectExtend(Cast, IsSigned, WI, SE, TD); 1154 } 1155 continue; 1156 } 1157 if (isSimpleIVUser(UseInst, L)) { 1158 pushIVUsers(UseInst, Simplified, SimpleIVUsers); 1159 } 1160 } 1161 if (WI.WidestNativeType) { 1162 WideIVMap[CurrIV] = WI; 1163 } 1164 } while(!LoopPhis.empty()); 1165 1166 for (std::map<PHINode *, WideIVInfo>::const_iterator I = WideIVMap.begin(), 1167 E = WideIVMap.end(); I != E; ++I) { 1168 WidenIV Widener(I->first, I->second, LI, SE, DT, DeadInsts); 1169 if (PHINode *WidePhi = Widener.CreateWideIV(Rewriter)) { 1170 Changed = true; 1171 LoopPhis.push_back(WidePhi); 1172 } 1173 } 1174 WideIVMap.clear(); 1175 } 1176} 1177 1178bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { 1179 // If LoopSimplify form is not available, stay out of trouble. Some notes: 1180 // - LSR currently only supports LoopSimplify-form loops. Indvars' 1181 // canonicalization can be a pessimization without LSR to "clean up" 1182 // afterwards. 1183 // - We depend on having a preheader; in particular, 1184 // Loop::getCanonicalInductionVariable only supports loops with preheaders, 1185 // and we're in trouble if we can't find the induction variable even when 1186 // we've manually inserted one. 1187 if (!L->isLoopSimplifyForm()) 1188 return false; 1189 1190 if (!DisableIVRewrite) 1191 IU = &getAnalysis<IVUsers>(); 1192 LI = &getAnalysis<LoopInfo>(); 1193 SE = &getAnalysis<ScalarEvolution>(); 1194 DT = &getAnalysis<DominatorTree>(); 1195 TD = getAnalysisIfAvailable<TargetData>(); 1196 1197 DeadInsts.clear(); 1198 Changed = false; 1199 1200 // If there are any floating-point recurrences, attempt to 1201 // transform them to use integer recurrences. 1202 RewriteNonIntegerIVs(L); 1203 1204 const SCEV *BackedgeTakenCount = SE->getBackedgeTakenCount(L); 1205 1206 // Create a rewriter object which we'll use to transform the code with. 1207 SCEVExpander Rewriter(*SE, "indvars"); 1208 1209 // Eliminate redundant IV users. 1210 // 1211 // Simplification works best when run before other consumers of SCEV. We 1212 // attempt to avoid evaluating SCEVs for sign/zero extend operations until 1213 // other expressions involving loop IVs have been evaluated. This helps SCEV 1214 // set no-wrap flags before normalizing sign/zero extension. 1215 if (DisableIVRewrite) { 1216 Rewriter.disableCanonicalMode(); 1217 SimplifyIVUsersNoRewrite(L, Rewriter); 1218 } 1219 1220 // Check to see if this loop has a computable loop-invariant execution count. 1221 // If so, this means that we can compute the final value of any expressions 1222 // that are recurrent in the loop, and substitute the exit values from the 1223 // loop into any instructions outside of the loop that use the final values of 1224 // the current expressions. 1225 // 1226 if (!isa<SCEVCouldNotCompute>(BackedgeTakenCount)) 1227 RewriteLoopExitValues(L, Rewriter); 1228 1229 // Eliminate redundant IV users. 1230 if (!DisableIVRewrite) 1231 SimplifyIVUsers(Rewriter); 1232 1233 // Compute the type of the largest recurrence expression, and decide whether 1234 // a canonical induction variable should be inserted. 1235 const Type *LargestType = 0; 1236 bool NeedCannIV = false; 1237 bool ExpandBECount = canExpandBackedgeTakenCount(L, SE); 1238 if (ExpandBECount) { 1239 // If we have a known trip count and a single exit block, we'll be 1240 // rewriting the loop exit test condition below, which requires a 1241 // canonical induction variable. 1242 NeedCannIV = true; 1243 const Type *Ty = BackedgeTakenCount->getType(); 1244 if (DisableIVRewrite) { 1245 // In this mode, SimplifyIVUsers may have already widened the IV used by 1246 // the backedge test and inserted a Trunc on the compare's operand. Get 1247 // the wider type to avoid creating a redundant narrow IV only used by the 1248 // loop test. 1249 LargestType = getBackedgeIVType(L); 1250 } 1251 if (!LargestType || 1252 SE->getTypeSizeInBits(Ty) > 1253 SE->getTypeSizeInBits(LargestType)) 1254 LargestType = SE->getEffectiveSCEVType(Ty); 1255 } 1256 if (!DisableIVRewrite) { 1257 for (IVUsers::const_iterator I = IU->begin(), E = IU->end(); I != E; ++I) { 1258 NeedCannIV = true; 1259 const Type *Ty = 1260 SE->getEffectiveSCEVType(I->getOperandValToReplace()->getType()); 1261 if (!LargestType || 1262 SE->getTypeSizeInBits(Ty) > 1263 SE->getTypeSizeInBits(LargestType)) 1264 LargestType = Ty; 1265 } 1266 } 1267 1268 // Now that we know the largest of the induction variable expressions 1269 // in this loop, insert a canonical induction variable of the largest size. 1270 PHINode *IndVar = 0; 1271 if (NeedCannIV) { 1272 // Check to see if the loop already has any canonical-looking induction 1273 // variables. If any are present and wider than the planned canonical 1274 // induction variable, temporarily remove them, so that the Rewriter 1275 // doesn't attempt to reuse them. 1276 SmallVector<PHINode *, 2> OldCannIVs; 1277 while (PHINode *OldCannIV = L->getCanonicalInductionVariable()) { 1278 if (SE->getTypeSizeInBits(OldCannIV->getType()) > 1279 SE->getTypeSizeInBits(LargestType)) 1280 OldCannIV->removeFromParent(); 1281 else 1282 break; 1283 OldCannIVs.push_back(OldCannIV); 1284 } 1285 1286 IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L, LargestType); 1287 1288 ++NumInserted; 1289 Changed = true; 1290 DEBUG(dbgs() << "INDVARS: New CanIV: " << *IndVar << '\n'); 1291 1292 // Now that the official induction variable is established, reinsert 1293 // any old canonical-looking variables after it so that the IR remains 1294 // consistent. They will be deleted as part of the dead-PHI deletion at 1295 // the end of the pass. 1296 while (!OldCannIVs.empty()) { 1297 PHINode *OldCannIV = OldCannIVs.pop_back_val(); 1298 OldCannIV->insertBefore(L->getHeader()->getFirstNonPHI()); 1299 } 1300 } 1301 1302 // If we have a trip count expression, rewrite the loop's exit condition 1303 // using it. We can currently only handle loops with a single exit. 1304 ICmpInst *NewICmp = 0; 1305 if (ExpandBECount) { 1306 assert(canExpandBackedgeTakenCount(L, SE) && 1307 "canonical IV disrupted BackedgeTaken expansion"); 1308 assert(NeedCannIV && 1309 "LinearFunctionTestReplace requires a canonical induction variable"); 1310 NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, 1311 Rewriter); 1312 } 1313 // Rewrite IV-derived expressions. 1314 if (!DisableIVRewrite) 1315 RewriteIVExpressions(L, Rewriter); 1316 1317 // Clear the rewriter cache, because values that are in the rewriter's cache 1318 // can be deleted in the loop below, causing the AssertingVH in the cache to 1319 // trigger. 1320 Rewriter.clear(); 1321 1322 // Now that we're done iterating through lists, clean up any instructions 1323 // which are now dead. 1324 while (!DeadInsts.empty()) 1325 if (Instruction *Inst = 1326 dyn_cast_or_null<Instruction>(&*DeadInsts.pop_back_val())) 1327 RecursivelyDeleteTriviallyDeadInstructions(Inst); 1328 1329 // The Rewriter may not be used from this point on. 1330 1331 // Loop-invariant instructions in the preheader that aren't used in the 1332 // loop may be sunk below the loop to reduce register pressure. 1333 SinkUnusedInvariants(L); 1334 1335 // For completeness, inform IVUsers of the IV use in the newly-created 1336 // loop exit test instruction. 1337 if (NewICmp && IU) 1338 IU->AddUsersIfInteresting(cast<Instruction>(NewICmp->getOperand(0))); 1339 1340 // Clean up dead instructions. 1341 Changed |= DeleteDeadPHIs(L->getHeader()); 1342 // Check a post-condition. 1343 assert(L->isLCSSAForm(*DT) && "Indvars did not leave the loop in lcssa form!"); 1344 return Changed; 1345} 1346 1347// FIXME: It is an extremely bad idea to indvar substitute anything more 1348// complex than affine induction variables. Doing so will put expensive 1349// polynomial evaluations inside of the loop, and the str reduction pass 1350// currently can only reduce affine polynomials. For now just disable 1351// indvar subst on anything more complex than an affine addrec, unless 1352// it can be expanded to a trivial value. 1353static bool isSafe(const SCEV *S, const Loop *L, ScalarEvolution *SE) { 1354 // Loop-invariant values are safe. 1355 if (SE->isLoopInvariant(S, L)) return true; 1356 1357 // Affine addrecs are safe. Non-affine are not, because LSR doesn't know how 1358 // to transform them into efficient code. 1359 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) 1360 return AR->isAffine(); 1361 1362 // An add is safe it all its operands are safe. 1363 if (const SCEVCommutativeExpr *Commutative = dyn_cast<SCEVCommutativeExpr>(S)) { 1364 for (SCEVCommutativeExpr::op_iterator I = Commutative->op_begin(), 1365 E = Commutative->op_end(); I != E; ++I) 1366 if (!isSafe(*I, L, SE)) return false; 1367 return true; 1368 } 1369 1370 // A cast is safe if its operand is. 1371 if (const SCEVCastExpr *C = dyn_cast<SCEVCastExpr>(S)) 1372 return isSafe(C->getOperand(), L, SE); 1373 1374 // A udiv is safe if its operands are. 1375 if (const SCEVUDivExpr *UD = dyn_cast<SCEVUDivExpr>(S)) 1376 return isSafe(UD->getLHS(), L, SE) && 1377 isSafe(UD->getRHS(), L, SE); 1378 1379 // SCEVUnknown is always safe. 1380 if (isa<SCEVUnknown>(S)) 1381 return true; 1382 1383 // Nothing else is safe. 1384 return false; 1385} 1386 1387void IndVarSimplify::RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter) { 1388 // Rewrite all induction variable expressions in terms of the canonical 1389 // induction variable. 1390 // 1391 // If there were induction variables of other sizes or offsets, manually 1392 // add the offsets to the primary induction variable and cast, avoiding 1393 // the need for the code evaluation methods to insert induction variables 1394 // of different sizes. 1395 for (IVUsers::iterator UI = IU->begin(), E = IU->end(); UI != E; ++UI) { 1396 Value *Op = UI->getOperandValToReplace(); 1397 const Type *UseTy = Op->getType(); 1398 Instruction *User = UI->getUser(); 1399 1400 // Compute the final addrec to expand into code. 1401 const SCEV *AR = IU->getReplacementExpr(*UI); 1402 1403 // Evaluate the expression out of the loop, if possible. 1404 if (!L->contains(UI->getUser())) { 1405 const SCEV *ExitVal = SE->getSCEVAtScope(AR, L->getParentLoop()); 1406 if (SE->isLoopInvariant(ExitVal, L)) 1407 AR = ExitVal; 1408 } 1409 1410 // FIXME: It is an extremely bad idea to indvar substitute anything more 1411 // complex than affine induction variables. Doing so will put expensive 1412 // polynomial evaluations inside of the loop, and the str reduction pass 1413 // currently can only reduce affine polynomials. For now just disable 1414 // indvar subst on anything more complex than an affine addrec, unless 1415 // it can be expanded to a trivial value. 1416 if (!isSafe(AR, L, SE)) 1417 continue; 1418 1419 // Determine the insertion point for this user. By default, insert 1420 // immediately before the user. The SCEVExpander class will automatically 1421 // hoist loop invariants out of the loop. For PHI nodes, there may be 1422 // multiple uses, so compute the nearest common dominator for the 1423 // incoming blocks. 1424 Instruction *InsertPt = User; 1425 if (PHINode *PHI = dyn_cast<PHINode>(InsertPt)) 1426 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) 1427 if (PHI->getIncomingValue(i) == Op) { 1428 if (InsertPt == User) 1429 InsertPt = PHI->getIncomingBlock(i)->getTerminator(); 1430 else 1431 InsertPt = 1432 DT->findNearestCommonDominator(InsertPt->getParent(), 1433 PHI->getIncomingBlock(i)) 1434 ->getTerminator(); 1435 } 1436 1437 // Now expand it into actual Instructions and patch it into place. 1438 Value *NewVal = Rewriter.expandCodeFor(AR, UseTy, InsertPt); 1439 1440 DEBUG(dbgs() << "INDVARS: Rewrote IV '" << *AR << "' " << *Op << '\n' 1441 << " into = " << *NewVal << "\n"); 1442 1443 if (!isValidRewrite(Op, NewVal)) { 1444 DeadInsts.push_back(NewVal); 1445 continue; 1446 } 1447 // Inform ScalarEvolution that this value is changing. The change doesn't 1448 // affect its value, but it does potentially affect which use lists the 1449 // value will be on after the replacement, which affects ScalarEvolution's 1450 // ability to walk use lists and drop dangling pointers when a value is 1451 // deleted. 1452 SE->forgetValue(User); 1453 1454 // Patch the new value into place. 1455 if (Op->hasName()) 1456 NewVal->takeName(Op); 1457 if (Instruction *NewValI = dyn_cast<Instruction>(NewVal)) 1458 NewValI->setDebugLoc(User->getDebugLoc()); 1459 User->replaceUsesOfWith(Op, NewVal); 1460 UI->setOperandValToReplace(NewVal); 1461 1462 ++NumRemoved; 1463 Changed = true; 1464 1465 // The old value may be dead now. 1466 DeadInsts.push_back(Op); 1467 } 1468} 1469 1470/// If there's a single exit block, sink any loop-invariant values that 1471/// were defined in the preheader but not used inside the loop into the 1472/// exit block to reduce register pressure in the loop. 1473void IndVarSimplify::SinkUnusedInvariants(Loop *L) { 1474 BasicBlock *ExitBlock = L->getExitBlock(); 1475 if (!ExitBlock) return; 1476 1477 BasicBlock *Preheader = L->getLoopPreheader(); 1478 if (!Preheader) return; 1479 1480 Instruction *InsertPt = ExitBlock->getFirstNonPHI(); 1481 BasicBlock::iterator I = Preheader->getTerminator(); 1482 while (I != Preheader->begin()) { 1483 --I; 1484 // New instructions were inserted at the end of the preheader. 1485 if (isa<PHINode>(I)) 1486 break; 1487 1488 // Don't move instructions which might have side effects, since the side 1489 // effects need to complete before instructions inside the loop. Also don't 1490 // move instructions which might read memory, since the loop may modify 1491 // memory. Note that it's okay if the instruction might have undefined 1492 // behavior: LoopSimplify guarantees that the preheader dominates the exit 1493 // block. 1494 if (I->mayHaveSideEffects() || I->mayReadFromMemory()) 1495 continue; 1496 1497 // Skip debug info intrinsics. 1498 if (isa<DbgInfoIntrinsic>(I)) 1499 continue; 1500 1501 // Don't sink static AllocaInsts out of the entry block, which would 1502 // turn them into dynamic allocas! 1503 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) 1504 if (AI->isStaticAlloca()) 1505 continue; 1506 1507 // Determine if there is a use in or before the loop (direct or 1508 // otherwise). 1509 bool UsedInLoop = false; 1510 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); 1511 UI != UE; ++UI) { 1512 User *U = *UI; 1513 BasicBlock *UseBB = cast<Instruction>(U)->getParent(); 1514 if (PHINode *P = dyn_cast<PHINode>(U)) { 1515 unsigned i = 1516 PHINode::getIncomingValueNumForOperand(UI.getOperandNo()); 1517 UseBB = P->getIncomingBlock(i); 1518 } 1519 if (UseBB == Preheader || L->contains(UseBB)) { 1520 UsedInLoop = true; 1521 break; 1522 } 1523 } 1524 1525 // If there is, the def must remain in the preheader. 1526 if (UsedInLoop) 1527 continue; 1528 1529 // Otherwise, sink it to the exit block. 1530 Instruction *ToMove = I; 1531 bool Done = false; 1532 1533 if (I != Preheader->begin()) { 1534 // Skip debug info intrinsics. 1535 do { 1536 --I; 1537 } while (isa<DbgInfoIntrinsic>(I) && I != Preheader->begin()); 1538 1539 if (isa<DbgInfoIntrinsic>(I) && I == Preheader->begin()) 1540 Done = true; 1541 } else { 1542 Done = true; 1543 } 1544 1545 ToMove->moveBefore(InsertPt); 1546 if (Done) break; 1547 InsertPt = ToMove; 1548 } 1549} 1550 1551/// ConvertToSInt - Convert APF to an integer, if possible. 1552static bool ConvertToSInt(const APFloat &APF, int64_t &IntVal) { 1553 bool isExact = false; 1554 if (&APF.getSemantics() == &APFloat::PPCDoubleDouble) 1555 return false; 1556 // See if we can convert this to an int64_t 1557 uint64_t UIntVal; 1558 if (APF.convertToInteger(&UIntVal, 64, true, APFloat::rmTowardZero, 1559 &isExact) != APFloat::opOK || !isExact) 1560 return false; 1561 IntVal = UIntVal; 1562 return true; 1563} 1564 1565/// HandleFloatingPointIV - If the loop has floating induction variable 1566/// then insert corresponding integer induction variable if possible. 1567/// For example, 1568/// for(double i = 0; i < 10000; ++i) 1569/// bar(i) 1570/// is converted into 1571/// for(int i = 0; i < 10000; ++i) 1572/// bar((double)i); 1573/// 1574void IndVarSimplify::HandleFloatingPointIV(Loop *L, PHINode *PN) { 1575 unsigned IncomingEdge = L->contains(PN->getIncomingBlock(0)); 1576 unsigned BackEdge = IncomingEdge^1; 1577 1578 // Check incoming value. 1579 ConstantFP *InitValueVal = 1580 dyn_cast<ConstantFP>(PN->getIncomingValue(IncomingEdge)); 1581 1582 int64_t InitValue; 1583 if (!InitValueVal || !ConvertToSInt(InitValueVal->getValueAPF(), InitValue)) 1584 return; 1585 1586 // Check IV increment. Reject this PN if increment operation is not 1587 // an add or increment value can not be represented by an integer. 1588 BinaryOperator *Incr = 1589 dyn_cast<BinaryOperator>(PN->getIncomingValue(BackEdge)); 1590 if (Incr == 0 || Incr->getOpcode() != Instruction::FAdd) return; 1591 1592 // If this is not an add of the PHI with a constantfp, or if the constant fp 1593 // is not an integer, bail out. 1594 ConstantFP *IncValueVal = dyn_cast<ConstantFP>(Incr->getOperand(1)); 1595 int64_t IncValue; 1596 if (IncValueVal == 0 || Incr->getOperand(0) != PN || 1597 !ConvertToSInt(IncValueVal->getValueAPF(), IncValue)) 1598 return; 1599 1600 // Check Incr uses. One user is PN and the other user is an exit condition 1601 // used by the conditional terminator. 1602 Value::use_iterator IncrUse = Incr->use_begin(); 1603 Instruction *U1 = cast<Instruction>(*IncrUse++); 1604 if (IncrUse == Incr->use_end()) return; 1605 Instruction *U2 = cast<Instruction>(*IncrUse++); 1606 if (IncrUse != Incr->use_end()) return; 1607 1608 // Find exit condition, which is an fcmp. If it doesn't exist, or if it isn't 1609 // only used by a branch, we can't transform it. 1610 FCmpInst *Compare = dyn_cast<FCmpInst>(U1); 1611 if (!Compare) 1612 Compare = dyn_cast<FCmpInst>(U2); 1613 if (Compare == 0 || !Compare->hasOneUse() || 1614 !isa<BranchInst>(Compare->use_back())) 1615 return; 1616 1617 BranchInst *TheBr = cast<BranchInst>(Compare->use_back()); 1618 1619 // We need to verify that the branch actually controls the iteration count 1620 // of the loop. If not, the new IV can overflow and no one will notice. 1621 // The branch block must be in the loop and one of the successors must be out 1622 // of the loop. 1623 assert(TheBr->isConditional() && "Can't use fcmp if not conditional"); 1624 if (!L->contains(TheBr->getParent()) || 1625 (L->contains(TheBr->getSuccessor(0)) && 1626 L->contains(TheBr->getSuccessor(1)))) 1627 return; 1628 1629 1630 // If it isn't a comparison with an integer-as-fp (the exit value), we can't 1631 // transform it. 1632 ConstantFP *ExitValueVal = dyn_cast<ConstantFP>(Compare->getOperand(1)); 1633 int64_t ExitValue; 1634 if (ExitValueVal == 0 || 1635 !ConvertToSInt(ExitValueVal->getValueAPF(), ExitValue)) 1636 return; 1637 1638 // Find new predicate for integer comparison. 1639 CmpInst::Predicate NewPred = CmpInst::BAD_ICMP_PREDICATE; 1640 switch (Compare->getPredicate()) { 1641 default: return; // Unknown comparison. 1642 case CmpInst::FCMP_OEQ: 1643 case CmpInst::FCMP_UEQ: NewPred = CmpInst::ICMP_EQ; break; 1644 case CmpInst::FCMP_ONE: 1645 case CmpInst::FCMP_UNE: NewPred = CmpInst::ICMP_NE; break; 1646 case CmpInst::FCMP_OGT: 1647 case CmpInst::FCMP_UGT: NewPred = CmpInst::ICMP_SGT; break; 1648 case CmpInst::FCMP_OGE: 1649 case CmpInst::FCMP_UGE: NewPred = CmpInst::ICMP_SGE; break; 1650 case CmpInst::FCMP_OLT: 1651 case CmpInst::FCMP_ULT: NewPred = CmpInst::ICMP_SLT; break; 1652 case CmpInst::FCMP_OLE: 1653 case CmpInst::FCMP_ULE: NewPred = CmpInst::ICMP_SLE; break; 1654 } 1655 1656 // We convert the floating point induction variable to a signed i32 value if 1657 // we can. This is only safe if the comparison will not overflow in a way 1658 // that won't be trapped by the integer equivalent operations. Check for this 1659 // now. 1660 // TODO: We could use i64 if it is native and the range requires it. 1661 1662 // The start/stride/exit values must all fit in signed i32. 1663 if (!isInt<32>(InitValue) || !isInt<32>(IncValue) || !isInt<32>(ExitValue)) 1664 return; 1665 1666 // If not actually striding (add x, 0.0), avoid touching the code. 1667 if (IncValue == 0) 1668 return; 1669 1670 // Positive and negative strides have different safety conditions. 1671 if (IncValue > 0) { 1672 // If we have a positive stride, we require the init to be less than the 1673 // exit value and an equality or less than comparison. 1674 if (InitValue >= ExitValue || 1675 NewPred == CmpInst::ICMP_SGT || NewPred == CmpInst::ICMP_SGE) 1676 return; 1677 1678 uint32_t Range = uint32_t(ExitValue-InitValue); 1679 if (NewPred == CmpInst::ICMP_SLE) { 1680 // Normalize SLE -> SLT, check for infinite loop. 1681 if (++Range == 0) return; // Range overflows. 1682 } 1683 1684 unsigned Leftover = Range % uint32_t(IncValue); 1685 1686 // If this is an equality comparison, we require that the strided value 1687 // exactly land on the exit value, otherwise the IV condition will wrap 1688 // around and do things the fp IV wouldn't. 1689 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && 1690 Leftover != 0) 1691 return; 1692 1693 // If the stride would wrap around the i32 before exiting, we can't 1694 // transform the IV. 1695 if (Leftover != 0 && int32_t(ExitValue+IncValue) < ExitValue) 1696 return; 1697 1698 } else { 1699 // If we have a negative stride, we require the init to be greater than the 1700 // exit value and an equality or greater than comparison. 1701 if (InitValue >= ExitValue || 1702 NewPred == CmpInst::ICMP_SLT || NewPred == CmpInst::ICMP_SLE) 1703 return; 1704 1705 uint32_t Range = uint32_t(InitValue-ExitValue); 1706 if (NewPred == CmpInst::ICMP_SGE) { 1707 // Normalize SGE -> SGT, check for infinite loop. 1708 if (++Range == 0) return; // Range overflows. 1709 } 1710 1711 unsigned Leftover = Range % uint32_t(-IncValue); 1712 1713 // If this is an equality comparison, we require that the strided value 1714 // exactly land on the exit value, otherwise the IV condition will wrap 1715 // around and do things the fp IV wouldn't. 1716 if ((NewPred == CmpInst::ICMP_EQ || NewPred == CmpInst::ICMP_NE) && 1717 Leftover != 0) 1718 return; 1719 1720 // If the stride would wrap around the i32 before exiting, we can't 1721 // transform the IV. 1722 if (Leftover != 0 && int32_t(ExitValue+IncValue) > ExitValue) 1723 return; 1724 } 1725 1726 const IntegerType *Int32Ty = Type::getInt32Ty(PN->getContext()); 1727 1728 // Insert new integer induction variable. 1729 PHINode *NewPHI = PHINode::Create(Int32Ty, 2, PN->getName()+".int", PN); 1730 NewPHI->addIncoming(ConstantInt::get(Int32Ty, InitValue), 1731 PN->getIncomingBlock(IncomingEdge)); 1732 1733 Value *NewAdd = 1734 BinaryOperator::CreateAdd(NewPHI, ConstantInt::get(Int32Ty, IncValue), 1735 Incr->getName()+".int", Incr); 1736 NewPHI->addIncoming(NewAdd, PN->getIncomingBlock(BackEdge)); 1737 1738 ICmpInst *NewCompare = new ICmpInst(TheBr, NewPred, NewAdd, 1739 ConstantInt::get(Int32Ty, ExitValue), 1740 Compare->getName()); 1741 1742 // In the following deletions, PN may become dead and may be deleted. 1743 // Use a WeakVH to observe whether this happens. 1744 WeakVH WeakPH = PN; 1745 1746 // Delete the old floating point exit comparison. The branch starts using the 1747 // new comparison. 1748 NewCompare->takeName(Compare); 1749 Compare->replaceAllUsesWith(NewCompare); 1750 RecursivelyDeleteTriviallyDeadInstructions(Compare); 1751 1752 // Delete the old floating point increment. 1753 Incr->replaceAllUsesWith(UndefValue::get(Incr->getType())); 1754 RecursivelyDeleteTriviallyDeadInstructions(Incr); 1755 1756 // If the FP induction variable still has uses, this is because something else 1757 // in the loop uses its value. In order to canonicalize the induction 1758 // variable, we chose to eliminate the IV and rewrite it in terms of an 1759 // int->fp cast. 1760 // 1761 // We give preference to sitofp over uitofp because it is faster on most 1762 // platforms. 1763 if (WeakPH) { 1764 Value *Conv = new SIToFPInst(NewPHI, PN->getType(), "indvar.conv", 1765 PN->getParent()->getFirstNonPHI()); 1766 PN->replaceAllUsesWith(Conv); 1767 RecursivelyDeleteTriviallyDeadInstructions(PN); 1768 } 1769 1770 // Add a new IVUsers entry for the newly-created integer PHI. 1771 if (IU) 1772 IU->AddUsersIfInteresting(NewPHI); 1773} 1774